Electric lamp having an undercoat for increasing the light output of a luminescent layer

Abstract

An electric lamp having a luminescent layer on the lamp envelope which produces visible light when impinged by ultraviolet radiation generated within the lamp. An undercoat for the luminescent layer increases the luminous efficacy of the lamp. The undercoat comprises an agglomerated particulate material of predominantly gamma alumina having a primary crystallite size of less than about 0.05 μm. The undercoat is effective to increase the luminous efficacy of certain fluorescent lamps so that they meet the minimum efficacy requirements of the Energy Policy Act of 1992.

I claim: 
     
       1. An electric lamp, comprising: a. a lamp envelope having an inner surface;   b. means within the lamp envelope for generating ultraviolet radiation;   c. a layer of a luminescent material adjacent the inner surface of the lamp envelope for generating visible light when impinged by said ultraviolet radiation; and   d. an other layer, between said inner surface of said lamp envelope and said layer of luminescent material, for reflecting ultraviolet radiation which has passed through said layer of luminescent material back into said luminescent material for increasing the visible light output of said luminescent material, said ultraviolet reflecting material comprising an agglomerated particulate material of predominantly gamma alumina having a primary crystallite size of less than about 0.05 μm, said ultraviolet reflecting layer of predominantly gamma alumina having a weight/surface area of between about 0.15 mg/cm 2  and about 0.30 mg/cm 2 .   
     
     
       2. A lamp according to claim 1, wherein said other layer is a base layer disposed directly on said inner surface of said lamp envelope. 
     
     
       3. A lamp according to claim 2, wherein said material has a primary crystallite size of about 0.01 μm. 
     
     
       4. A lamp according to claim 3, wherein said layer of luminescent material comprises a halophosphate phosphor. 
     
     
       5. A lamp according to claim 3, wherein said lamp is an F96T12 fluorescent lamp having an efficacy of at least 80 LPW. 
     
     
       6. A lamp according to claim 3, wherein said lamp is an F40T12 fluorescent lamp having an efficacy of at least 75 LPW. 
     
     
       7. A lamp according to claim 2, wherein said layer of luminescent material comprises a halophosphate phosphor. 
     
     
       8. A lamp according to claim 1, wherein said layer of luminescent material comprises a halophosphate phosphor. 
     
     
       9. A lamp according to claim 8, wherein said lamp is an F96T12 fluorescent lamp having an efficacy of at least 80 LPW. 
     
     
       10. A lamp according to claim 8, wherein said lamp is an F40T12 fluorescent lamp having an efficacy of at least 75 LPW. 
     
     
       11. A lamp according to claim 1, wherein said material has a primary crystallite size of about 0.01 μm. 
     
     
       12. A lamp according to claim 1, wherein said means for generating ultraviolet radiation is comprised by an arc tube disposed within said lamp envelope, said arc tube including a filling of an ionizable material and a rare gas and a pair of discharge electrodes between which a discharge takes place during lamp operation. 
     
     
       13. A lamp according to claim 1, wherein said means for generating ultraviolet radiation comprises a filling of an ionizable material and a rare gas within said lamp envelope and a pair of discharge electrodes each adjacent a respective sealed end of said discharge vessel. 
     
     
       14. A low pressure mercury vapor fluorescent lamp, comprising: a. a tubular, light transmissive lamp envelope having opposing sealed ends and an inner tubular surface;   b. a filling of mercury and a rare gas;   c. a pair of discharge electrodes each arranged at a respective sealed end of said lamp envelope;   d. means for connecting said discharge electrodes to a source of electric potential outside of said lamp envelope, whereby during lamp operation a gas discharge is maintained between said discharge electrodes, which gas discharge emits ultraviolet radiation;   e. a first, light transmissive and ultraviolet radiation reflecting layer disposed on said inner surface of said lamp envelope, said first layer comprising an agglomerated particulate material of predominantly gamma alumina having a primary crystallite size of about 0.01 μm, said first layer of material having a weight/surface area of between about 0.15 mg/cm 2  and about 0.3 mg/cm 2  ; and   f. a second, layer of luminescent material disposed on said first layer.   
     
     
       15. A lamp according to claim 14, wherein said layer of luminescent material comprises a halophosphate phosphor. 
     
     
       16. A lamp according to claim 15, wherein said lamp is an F96T12 fluorescent lamp having an efficacy of at least 80 LPW. 
     
     
       17. A lamp according to claim 15, wherein said lamp is an F40T12 fluorescent lamp having an efficacy of at least 75 LPW. 
     
     
       18. An electric lamp, comprising: a. a lamp envelope having an inner surface;   b. means within the lamp envelope for generating ultraviolet radiation;   c. a layer of a luminescent material adjacent the inner surface of the lamp envelope for generating visible light when impinged by said ultraviolet radiation; and   d. an other layer, between said inner surface of said lamp envelope and said layer of luminescent material, for reflecting ultraviolet radiation which has passed through said layer of luminescent material back into said luminescent material for increasing the visible light output of said luminescent material, said ultraviolet reflecting material comprising an agglomerated particulate material having a primary crystallite size of less than about 0.05 μm, and having a weight/ surface area of between about 0.15mg/cm 2  and about 0.30 mg/cm 2 .   
     
     
       19. A lamp according to claim 18, wherein said other layer is a base layer disposed directly on said inner surface of said lamp envelope. 
     
     
       20. A lamp according to claim 18, wherein said material has a primary crystallite size of about 0.01 μm.